How to remove a node from a frame?
This is a simple one keyboard shortcut thing to do. With the "trapped" node, or nodes selected press AltP. 

As the manual says:


  To remove them select the node(s) and use the Alt-P shortcut. This uses the same default keyboard bindings as Parenting and can be thought of as a similar concept.




If you really wanted to, you could always delete the frame node with Delete which would leave any nodes that were in the frame in place (the nodes inside the frame do not get deleted unless they are selected too).

Also you do not have to drop the nodes over the frame to get them in the frame. With the nodes selected and the frame active, press CtrlP (keeping with the parenting concept) to add them to the active frame.